1. Field of the Invention
The present invention relates to read elements for recording heads for use with magnetic recording media. Specifically, the invention relates to a combined shield/electrical lead for the read element having minimized Anisotropic Magneto-Resistance (AMR) effect.
2. Description of the Related Art
Magneto-resistive (MR) and giant magneto-resistive (GMR) read elements for reading from magnetic recording media have been proposed to overcome the limited sensitivity of inductive reading GMR read elements are generally composed of alternating layers of magnetic and nonmagnetic material, so that, when exposed to a magnetic field, the relative change in the orientation of the magnetizations in the magnetic layers alters the spin dependent scattering of conduction electrons, thereby increasing or decreasing the resistance of the GMR head to an applied sense current. A constant resistance level indicates a binary xe2x80x9c0,xe2x80x9d and a changing resistance level indicates a binary xe2x80x9c1.xe2x80x9d
Spin valves have also been used to increase the read sensitivity of recording heads. A typical spin valve comprises a pair of ferromagnetic layers having a nonmagnetic layer therebetween, with an antiferromagnetic layer adjacent to one of the ferromagnetic layers. The antiferromagnetic layer is a material that is generally not affected by external magnetic fields, and is therefore generally considered to be nonmagnetic. However, the material has been annealed at high temperature and cooled while exposed to a magnetic field. The magnetization in the ferromagnetic layer closest to the antiferromagnetic layer will align itself with respect to the orientation of the closest layer of the antiferromagnetic material. The combination of the ferromagnetic layer and adjacent antiferromagnetic layer is commonly known as the pinned layer, with the opposite ferromagnetic layer known as the free layer. When the spin valve is exposed to a magnetic field, the orientation of the magnetiationof the free layer will change to correspond with this magnetic field. This relative change in the orientation of the magnetization of the free layer will alter the spin dependent scattering of conduction electrons, thereby increasing or decreasing the resistance of the spin valve to an applied sense current. As before, a constant resistance level indicates a binary xe2x80x9c0xe2x80x9d and the changing resistance level indicates a binary xe2x80x9c1.xe2x80x9d
Read elements are located between a pair of ferromagnetic shields for preventing the read element from being influenced by magnetic domains adjacent to the domain currently being read. The sense current for detecting changes in the resistance of the read element is applied through a pair of leads on opposing sides of the read element. This sense current may be applied either parallel to the plane of the alternating layers within the read element (CIP), or perpendicular to the plane of these alternating layers (CPP). To minimize the resistance of the electrical leads, these leads must be thick. Additionally, a typical ferromagnetic shield will exhibit an Anisotropic Magneto-Resistance (AMR) effect, wherein the resistance of the shield will change if its magnetization direction changes. Therefore, a thick insulation must be provided between the electrical leads for the read element and the ferromagnetic shields to prevent any sense current from flowing through the shields, thereby causing both changes in the resistance of the read element and changes in the resistance of the shields to be detected. The resulting sequence of thick layers increases the distance from one shield to the other, thereby reducing the maximum linear bit density within the corresponding magnetic recording media.
Accordingly, there is a need for a magnetic recording head having reduced distance between the magnetic shields for its read elements. Additionally, there is a need for a magnetic shield material having a minimized AMR effect.
The present invention is an improved recording head for use with magnetic recording media. The improved recording head includes a read element having a pair of shields for which the anisotropic magneto-resistance effect has been minimized, thereby permitting the shields to serve the additional purpose of electrical leads for the read element.
A preferred embodiment of the present invention includes a recording head combining a read portion and a write portion. The write portion may be of either perpendicular or longitudinal configuration. A typical perpendicular recording head includes a main pole, an opposing pole magnetically coupled to the main pole, and an electrically conductive coil adjacent to the main pole. The bottom of the opposing pole will typically have a surface area greatly exceeding the surface area of the main pole""s tip. Likewise, a typical longitudinal recording head includes a pair of poles, with a coil adjacent to one pole. Unlike a perpendicular recording head, a longitudinal recording head will typically use poles having bottom surfaces with substantially equal areas. In either case, electrical current flowing through the coil creates a flux through the main pole. The direction of the flux may be reversed by reversing the direction of current flow through the coil.
In some preferred embodiments, the opposing pole of the perpendicular head (or the first pole of the longitudinal head) can also form one of two substantially identical shields for the read elements, which are parallel to the trackwidth The read element is located between these shields. The shields also form electrical leads for the read elements, thereby eliminating the necessity of a separate electrical lead, and insulation between the electrical lead and the magnetic shield.
Presently available magnetic shields are generally combinations of Ni, Fe, and Co. Such magnetic shields have too much variation in resistance with changing magnetization direction within the material. This is known as the Anisotropic Magneto-Resistance (AMR) effect. A sense current passing through these combination lead/shields and the read element would measure the change in resistance not only in the read elements, but also within the lead/shields. Therefore, a lead/shield of the present invention includes additional elements that will reduce the AMR effect. Examples of additional materials include Cu, Cr, Mn, Ti, Au, Ag, V, Zr, Nb, Ta, and W. Preferred embodiments of lead/shields of the present invention include both alloys of these elements within the crystal structure of the magnetic shields material, and laminated structures wherein these elements are layered within the magnetic shields. Another preferred embodiment may include a separate, low resistivity lead outside the lead/shields, on opposing sides of the read element and associated shields. The low resistance of these leads will cause current to travel through these leads instead of through the magnetic shields for the maximum distance possible, traveling through the shields for the smallest distance possible. This will result in current flowing through the magnetic shields perpendicular to the surface of the read element, thereby yielding constant shield resistance.
Although the present invention may be used with any presently known read elements, it is particularly useful with low resistance read elements such as giant magneto-resistive (GMR) elements and spin valves. The invention may still be used with high resistance read elements such as tunnel magneto-resistive (TMR) read elements.
GMR read elements are generally composed of alternating layers of magnetic and nonmagnetic material, so that, when exposed to a magnetic field, the relative change in the orientation of the magnetizations in the magnetic layers alters the spin dependent scattering of conduction electrons, thereby increasing or decreasing the resistance of the GMR head to an applied sense current. A constant resistance level generally indicates a binary xe2x80x9c0,xe2x80x9d and a changing resistance level generally indicates a binary xe2x80x9c1.xe2x80x9d
A typical spin valve comprises a pair of ferromagnetic layers having a nonmagnetic layer therebetween, with an antiferromagnetic layer adjacent to one of the ferromagnetic layers. The antiferromagnetic layer is a material that is generally not affected by external magnetic fields, and is therefore generally considered to be nonmagnetic. However, the material has been annealed at high temperature and cooled while exposed to a magnetic field. The magnetization in the ferromagnetic layer closest to the antiferromagnetic layer will align itself with respect to the orientation of the closest layer of the antiferromagnetic material. The combination of the ferromagnetic layer and adjacent antiferromagnetic layer is commonly known as the pinned layer, with the opposite ferromagnetic layer known as the free layer. When the spin valve is exposed to a magnetic field, the orientation of the magnetic field within the free layer will change to correspond with this magnetic field. This relative change in the orientation of the magnetizations within the free layer will alter the spin dependent scattering of conduction electrons, thereby increasing or decreasing the resistance of the spin valve to an applied sense current. As before, a constant resistance level generally indicates a binary xe2x80x9c0xe2x80x9d and the changing resistance level generally indicates a binary xe2x80x9c1.xe2x80x9d
Tunnel magneto-resistive read elements include a pair of ferromagnetic layers with a nonmagnetic insulator such as alumina oxide therebetween. An antiferromagnetic layer is adjacent to one of the two ferromagnetic layers. The operation of a TMR read element is similar to that of a spin valve.
A typical magnetic recording medium includes a first layer having a plurality of magnetically permeable tracks separated by nonmagnetized transitions. If perpendicular recording is desired, the magnetic recording medium may include a magnetically permeable lower layer. The lower layer is magnetically soft relative to the tracks.
To read from the magnetic recording medium, the recording head is separated from the magnetic recording medium by the flying height. The magnetic recording medium is moved past the recording heads so that the recording head follows the tracks of the magnetic recording medium, typically with the magnetic recording medium first passing under one shield, followed by the read element, then passing under the write portion of the recording head. As the magnetic recording medium passes under the read element, the magnetic fields within the recording medium orient the adjacent magnetization within the ferromagnetic read element layers so that they are either parallel (corresponding to minimum resistance) or antiparallel (corresponding to maximum resistance), depending on the direction of the magnetic field being read from the recording medium. A sense current is passed through the GMR element by a pair of electrical contacts, thereby enabling the read element""s resistance to be detected. A constant level of resistance is read as a binary xe2x80x9c0,xe2x80x9d and a changing resistance is read as a binary xe2x80x9c1.xe2x80x9d
Other proposed recording heads using separate electrical leads and magnetic shields for the read element require the use of thick electrical leads to provide minimum resistance for the sense current. Additionally, the high AMR effect of presently known magnetic shields requires that sense current be prevented from traveling through the magnetic shields within prior art recording heads. Isolating the sense current from the magnetic shields requires thick insulation between the electrical leads and the magnetic shields. These additional layers between the opposing magnetic shields increases the distance between the magnetic shields. The distance between adjacent magnetic domains within a track of the magnetic recording medium must be sufficiently large so that the magnetic shields on either side of the read element will prevent the read element from being influenced by magnetic fields adjacent to the magnetic fields currently being read. Therefore, a large distance between the opposing magnetic shields limits the recording density which may be used. By combining the magnetic shields and electrical leads into a single component, the present invention reduces the distance between the magnetic shields, thereby increasing the permissible recording density.
It is therefore an aspect of the present invention to provide a recording head for use with magnetic recording media wherein the shields on either side of the read element also form the electrical leads for the read element.
It is another aspect of the present invention to provide a recording head for use with magnetic recording media having a minimized distance between the shields surrounding the read element.
It is a further aspect of the present invention to provide a magnetic recording head for use with magnetic recording media having shields with a minimized AMR effect.
It is another aspect of the present invention to provide a pair of shields for use within a magnetic recording head with a first material component having ferromagnetic properties, and a second material component having electroconductive properties, and wherein the second material component reduces the AMR effect within the first material.
It is a further aspect of the present invention to provide a magnetic recording head wherein the electrical leads for the read elements are located outside the read elements"" shields, thereby causing the sense current to flow through the shields perpendicular to magnetic fields within the shields.
These and other aspects of the present invention will become more apparent through the following description and drawings.